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Unformatted text preview: k out the time of day, date, and so on. Normally this is a small battery-backed system with a low frequency crystal oscillator which runs all the time, even when the computer itself is turned off. RTL Register Transfer Level; an abstract view of a hardware system such as a processor where multi-bit values are viewed as flowing between registers along buses. RTOS Real-Time Operating System; an operating system that supports programs that must satisfy external timing constraints. These are often small (a few kilobytes) and well suited to use in embedded systems. SDLC Synchronous Data Link Controller; a peripheral that connects a computer to a clocked serial interface and supports one or more standard protocols. SoC System-on-Chip; a single integrated circuit that incorporates all of the functionality of an electronic system, including the processor, memory and peripherals. At the time of writing most SoCs still require off-chip memory resources in addition to their on-chip memory, but all other system components are on chip. SPSR Saved Program Status Register, an ARM register used to save the values of the CPSR when an exception occurs. SRAM Static Random Access Memory; more expensive than DRAM, this form of RAM holds its data in flip-flops which do not require refreshing. SRAM has a lower access time than DRAM and can retain its contents indefinitely with almost no power dissipation. It is used for most RAM functions on processor chips, such as cache and TLB Glossary 409 memory, and may be used for the main memory in some smaller embedded systems. TLB Translation Look-aside Buffer, a cache of recently used page table entries which avoids the overhead of page table-walking on every memory access. UART Universal Asynchronous Receiver/Transmitter; a peripheral device that interfaces a serial line (typically with an RS232 signalling protocol) to a processor bus. USB Universal Serial Bus; a standard interface on more recent PCs that supports the connection of various peripherals. It uses a high-speed serial protocol and an electrical interface that allows devices to be connected and disconnected while the machine is running (that is, it is 'hot-pluggable'). VHDL VHSIC Hardware Description Language (where VHSIC expands to Very High-Speed Integrated Circuit); a standard lang...
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- Spring '09